This invention relates to a secondary air supply system for an engine and more particularly to an improved arrangement for assisting in the cleaning of the exhaust gases of an internal combustion engine.
It has been acknowledged that the addition of a supply of secondary air to the exhaust system can be helpful in reducing the emission of unwanted exhaust gas constituents. If the secondary air is added at a place close enough to the exhaust port and where the exhaust gases still have a high temperature, the added air can complete the combustion of any unburned hydrocarbons and also can convert carbon monoxide into carbon dioxide.
One way in which such secondary air is supplied is through the use of an air bleed passage that will supply air to the exhaust port in proximity to the exhaust valve. In order to preclude reverse flow through the secondary air passages, there are normally provided the one way check valves that permit air to flow into the exhaust system but will not permit the exhaust gases to escape to the atmosphere.
As is well known, these check valves are sensitive to temperature and, therefore, it is normally the practice to position the check valve at some distance from the actual exhaust port. By so spacing the check valve, it can be protected from the heat of the engine exhaust. However, this also gives rise to a rather large volume in which air may become trapped and which is at a lower temperature than the exhaust gases. The exhaust gases contain a large amount of water and also hydrocarbons in vapor form and this water can condense in the secondary air supply system between the check valve and the exhaust port. In some situations the condensed vapor may even reach the check valve. This presents obvious problems of potential corrosion.
It is, therefore, a principal object of this invention to provide an improved secondary air supply system for an engine. It is a further object of this invention to provide an engine secondary air system wherein the check valve that controls the flow through the secondary air passage is protected from the heat and the arrangement is such that condensed vapors cannot remain in the air supply conduit.
It should be readily apparent that the use of check valves for controlling the flow of secondary air also presents a potential noise problem. That is, when these valves rapidly open and close they can emit noise which may be objectionable. This problem is particularly acute with certain types of open vehicles like motorcycles wherein the engine is exposed and wherein the air system and check valve may not be placed at a great distance from the rider.
It is, therefore, a still further object of this invention to provide an improved secondary air system for a vehicle wherein the check valves are positioned so that the noise that they emanate will reach the rider.